1. Field of the Invention
The present invention relates to a nitride semiconductor light emitting device with improved light efficiency, more specifically to a nitride semiconductor light emitting device with improved light efficiency in which a hole injection efficiency from a p-type nitride layer to an active layer is improved through forming a superlattice layer with asymmetrical structure by changing a thickness of well layers or a height of barrier layers between an active layer and p-type nitride layer.
2. Discussion of the Background
In general, III elements such as Gallium Nitride (GaN), Aluminum Nitride (AlN), and Indium Gallium Nitride (InGaN) used for a nitride semiconductor emitting device are excellent in thermal stability and have an energy band structure with a direct band gap, and they recently came into the spotlight for blue and ultraviolet rays photoelectric element fields. Specially, a semiconductor with Gallium Nitride (GaN) receives attention through its narrowed energy band. A light emitting device using Gallium Nitride (GaN) based semiconductor is used in a flat panel display with large size and natural color, a traffic light, an internal lighting device, a light source with high density, an output system with high resolution, and an optical communication.
Thus, also an amount of driving current is varied since a nitride semiconductor light emitting device is used in various fields. In case of a mobile phone, it is operated in a low current such as 20 mA, but in case of backlight unit and lighting device with high output, it is operated in a current more than 100 mA or more than 350 mA.
In general, a carrier density of light emitting device increases as driving current increases, herein, an electron is not combined with a hole in a multi-quantum well and an electron overflow phenomenon to a p-type nitride layer is occurred.
In order to solve this problem, an electron blocking layer is formed between an active layer and a p-type nitride layer in a structure of light emitting device. An energy band of an electron blocking layer is large enough than a quantum well of an active layer, and overflow to p-type nitride layer without combination is prevented.
However, there is a problem that a hole injection efficiency is decreased since the electron blocking layer also affects a hole as an energy barrier which is provided from a p-type nitride layer to an active layer.